My 87 pathfinder idles rough and lacks power, can only go up hill at about 25mph, some one said to look at the timming belt and check crank pully for sloppiness is this an easy fix if there is slop?

I would start with simple things first. Check your spark plugs, wires, cap and rotor to make sure they are working properly. The next thing i would check is the fuel system. A malfunctioning pump or dirty fuel filter would make your engine run poorly. You can also check your air intake system (filter, mass air flow meter (if you have one)) If that looks ok, you might also have a vacuum leak on one of the hoses somewhere too. Check that stuff first and let us know what you find.